Custom Form/Field Sharing Restrictions

We would find it beneficial to be able to lock-down custom forms so that they, and the fields within, can only be edited by certain groups or individuals. We have encountered a couple scenarios where we want a custom form on a project that we do not want the PM/Project Owner to be able to modify - it is instead something only Accounting or Finance should be able to modify. Unfortunately, with the way Project sharing and permissions work today, this is not possible.